In the manufacturing of color negative photographic printing papers, at least three light sensitive emulsion layers are used to capture the photographic image, i.e., red, green, and blue. Frequently, the blue sensitive emulsion is placed at the bottom of the light sensitive multilayer coating pack. In this layering order, less light is available to the bottom blue layer because of the light scattering and absorption occuring in the layers above.
The incandescent lamp used for exposing the paper is low in its energy output in the short wavelength region (blue) of the visible spectra. This further reduces the energy impinging on the blue layer.
The color negative film through which the light is exposed onto the photographic paper has a yellowish brown tint (as a result of the processing used for development). This yellowish background filters out blue light causing a further diminution of blue light arriving at the bottom layer.
Still, in recent developments in the art of manufacturing color photographic paper, there is a need to improve the color reproduction of the original scene as captured in the color negative film. One way of achieving such an improvement is to employ a shorter blue spectral sensitizing dye that better matches the blue sensitization of the original film (U.S. Ser. No. 245,336 filed May 18, 1994). As a result, the sensitivity of the blue emulsion is further pushed towards the shorter wavelength region where less light energy is available.
Consequently, there exists a need to manufacture a blue sensitive emulsion that has a high sensitivity (speed) in order to overcome the light deficiency and to capture the fidelity of the original color image.
Photofinishers also desire short processing times in order to increase the output of color prints. One way of increasing output is to accelerate the development by increasing the chloride content of the emulsions; the higher the chloride content, the higher the development rate. Furthermore, the release of chloride ion into the developing solution has less restraining action on development compared to bromide, thus allowing developing solutions to be utilized in a manner that reduces the amount of waste developing solution.
Additionally, it is highly desirable that color negative printing papers have speed characteristics that are invariant with exposure time. This feature allows their usage in a wide variety of applications, including high speed printers, easel printing, and other electronic printing devices. To accommodate this variety of exposing devices, the emulsions used in the color negative papers must be capable of recording the exposure between the exposure range of nanoseconds (1.times.10.sup.-9 seconds) to several minutes while maintaining printing speed and contrast. But emulsions with high-chloride content are usually less efficient, with relative efficiency being worse at high intensity-short time exposures. Therefore, there is a need for high-chloride emulsions with high sensitivity that exhibit little loss in speed at extremely short exposure times.
Another factor to be considered when designing a color paper is print quality such that it is pleasing to the eye both in color and contrast. A color paper with high contrast gives saturated colors and rich with details in shadow areas.
It is known in the art that the greater reducibility and developability of silver chloride relative to silver bromide or iodide emulsions make silver chloride emulsion highly susceptible to fog formation. Thus, it is critical when using silver chloride emulsions of high sensitivity that this fog be restrained.
It is also known in the art that when fog is generated during the precipitation stage, certain agents can be added in this process to reduce the undesirable minute silver clusters that constitute this fog. These agents include hydrogen peroxide, peroxy acid salts, disulfides (U.S. Pat. No. 3,397,986), mercury compounds (U.S. Pat. No. 2,728,664) and iodine. EP 576,920 claims the use of iodine in controlling fog from precipitation of core-shell bromoiodide emulsions. EP 563,708; EP 562,476; EP 561,415; and JP 06,011,784 claim the use of iodide releasing agents during precipitation for controlling fog in tabular AgBrI emulsions.
Iodonium salts are alleged in JP 04,090,547 by Konica and in U.S. Pat. No. 5,085,972 by 3M to be useful in waterless presensitized lithographic plates. 3M claimed the use of iodonium salts as photoinitiators in photopolymerizable compositions in U.S. Pat. No. 5,086,192, U.S. Pat. No. 4,791,045 and in photosensitive compositions for positive image formation in U.S. Pat. No. 4,701,402, U.S. Pat. No. 4,507,497 and U.S. Pat. No. 4,394,403. The Agency of Industrial Sciences and Technology of Japan disclosed the use of iodonium salts in photoimaging resin compositions in JP 60,071,657; in visual light-sensitive photopolymerizing resin composition in JP 60,076,740; in photosensitive compositions in JP 60,049,334; in photocuring resin compositions in JP 60,078,442 and JP 60,076,735 and in photoinsolubilizing resin compositions in JP 60,078,443. The use of iodonium salts in photosensitive materials for electrophotography is described in JP 49/027,444. U.S. Pat. No. 3,554,758 claimed the use of double salts of Hg(II) with iodonium salts as antifoggants in AgBrI emulsions. Diphenyliodonium salts have been claimed for use in lith-type emulsions with bromide content of at least 5%. Diphenyl iodonium nitrate is alleged in U.S. Pat. No. 2,105,274 to be useful in reducing yellow stain in a silver chloride emulsion. Diphenyl iodonium chloride is alleged to be useful in silver bromiodide emulsions with bromide content of at least 50% in U.S. Pat. No. 3,947,273.